TXRF 2007 18-22.06.2007 Povo(Trento) Italy
oral contribution
Quantitative TXRF analysis of metallic contamination on various
nanoelectronic surfaces
M. Veillerota, A. Danel a, T. Lardina, Y. Bordeb, H. Kohnoc, M. Yamagamic
a
CEA-LETI, MINATEC, 17 rue des Martyrs, 38054 Grenoble cedex 9, France. Fax: +33 438 785 273; Tel:
+33 438 784 193; E-mail: marc;veillerot@cea.fr
b
ST Microelectronics, 850 rue J. Monnet, 38926 Crolles cedex, France.
c
Rigaku Corporation, 14-8 Akaoji-cho, Takatsuki-shi, Osaka 569-1146, Japan.
Introduction
The need of accurate control of contamination in advanced microelectronic manufacturing is
necessary to achieve high yield and short cycle time. Thanks to multiple advantages such as user
friendliness, very good analytical capabilities (low limit of detection in the E10 at/cm2 range, Na to U
detection using multiple X-ray excitations on the same equipment), non invasive measurement,
acceptable throughput, full wafer mapping; TXRF appears today as the method of choice for metallic
contamination monitoring [1].
If many relevant information for trace analysis on Si wafers are today available, nanoelectronic
pushes the fast introduction of new (“non –Si”) substrates and layers [2] on which TXRF analysis can
be a challenge. Two issues recently reported in literature are the strong overlaps we face when the
surface to be measured contains heavy elements, such as Hf in high-k films [3], and the calibration for
quantitative analysis [4].
This study will discuss TXRF calibration for quantitative analysis of trace of metals on non –Si
layers and substrates.
TXRF set up
For ultra trace application, the equipment should be used under its best signal to noise ratio (SNR)
configuration. This depends on the surface and element analyzed. The main parameters impacting the
SNR for a given tool and acquisition time are the incident angle (i) and the dead time during
counting. This is illustrated in figure 1 with the measurement of a Ni contaminated Si wafer, where the
SNR was calculated with the low limit of detection (LLD) of Ni:
LLD  3
C Ni
I net
I BG
t net
where CNi is the Ni concentration, Inet the net TXRF signal and IBG the background at the fluorescence
energy of Ni (in count par sec.; cps), and tnet the net integration time in sec. = tset(1-DT) with DT the
dead time.
In this work, a ‘Fab300’ equipment from Rigaku using a W rotating anode with 3 optics to select
the W-M (1.77 keV) or W-L (9.67 keV) line, or a fraction of the spectrum at high energy (24 keV)
as the excitation beam, with i setup at about c/2.
Quantitative analysis issues
A first quantification issue is the selection of i and the consequence of this setup on quantitative
analysis of contaminants having various shapes. As shown in figure 1, a good SNR region is obtained
between 0.5 c and c. Thus, TXRF users can select i  c / 2 as the theoretical iso-quantification
angle for various types of contamination (film or particulate [1]), or i  c / 2 to minimize the
intensity of the major peaks (i.e. from substrate and from the X-ray source) and then minimize
background degradation on elements with a fluorescence close to these main peaks (Cu K overlap
Book of Abstracts TXRF2007 © FondazioneBrunoKessler-irst 2007
session | 1
oral contribution
TXRF 2007 18-22.06.2007 Povo(Trento) Italy
with the escape peak of W-L as an example). The full extend of this paper will discuss the issue of i
selection more in details.
The second quantification issue is related to calibration samples. Today, TXRF in IC manufacturing,
mainly applied on Si wafers, suffers from the lack of certified standard samples. Calibration must be
performed using samples with dried residues (the amount of a given standard element being known) or
samples uniformly contaminated, with the level of contamination certified by a reference method, such
as VPD-ICPMS. The limitations of these protocols applied to Si and non Si surfaces will be presented
in the full extend of the paper. A specific emphasis will be given on the possible use of Si
contaminated wafers for the calibration of non Si applications.
Signal to noise ratio expressed as the detection limit (at/cm 2)
1.00E+13
1.00E+12
1.00E+11
1.00E+10
0
0.1
best signal
to noise ratio
0.2
c
0.3
0.4
0.5
Incident angle (°)
Figure 1. Signal to noise ratio obtained on a Ni contaminated Si wafer (31013 Ni at/cm2, W-L excitation).
References
[1] D. Hellin et al., “Trends in total reflection X-ray fluorescence spectrometry for metallic contamination
control in semiconductor nanotechnology”, Spectrochemica Acta part B, 61, (2006), pp. 496.
[2] International Technology Roadmaps for Semiconductor industry, http://public.itrs.net, 2005.
[3] C. Sparks et al., “Advanced TXRF Analysis: Mapping Metallic Contamination and Background Reduction
for Measurements on High-k Materials”, presented at UCPSS 2006, to be published in to be published in Solid
State Phenomena 2007.
[4] D. Hellin et al., “Determination of metallic contaminants on Ge wafers using direct and droplet sandwich
etch TXRF”, Spectrochemica Acta part B, 60, (2005), pp. 209.
Book of Abstracts TXRF2007 © FondazioneBrunoKessler-irst 2007
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